Steel makers are increasingly shaped by the forces of globalization. Increasingly, steel companies are turning to maintenance and service companies to help them develop solutions that will reduce furnace downtimes, reduce costs and improve on mill safety. Many of their maintenance systems are manual, time consuming and have an unacceptably high operator injury rate. Improved maintenance techniques and equipment can improve efficiency and advance technology.
A tuyere is a nozzle through which air and other gases are blown into a blast furnace via a blow pipe under pressure from a blast engine or other device. Injection through the tuyere creates furnace temperatures far higher than could be normally achieved. A modern blast furnace contains 24 to 36 tuyeres. Tuyeres are constructed from pure copper and cooled with internal water pipes to withstand the extreme temperatures. A typical tuyere measures 18 in. in end diameter on the intake end, 6¼in. to 7¾in. diameter at the nose end and are approximately 21 in. in length. They are very heavy and pressed hydraulically into a cooler inserted in a tymp (hollow water-cooled iron cushing) in the furnace wall to a pressure of 5000 lb. The noses can be heavily damaged by the furnace environment and removing a heavy, damaged tuyere press-fit into the cooler is no small task, especially for a manual system.
Compounding the challenge is the demanding environment of the tuyeres and the often limited space in which to access the tuyeres for installation and maintenance The life of a tuyere varies (from several days to several months) and can breakdown by burning and deformation of the tuyere walls caused by materials, such as skull, in the furnace environment. The loss can often be catastrophic in the case of water leakage which results in molten iron and gases escaping the pressurized furnace. A ten minute break out can result in a multimillion dollar loss and days of furnace down time. The replacement of one single tuyere without a break out typically interrupts the operation of the furnace for one hour or more, depending on the length of time the tuyere has been in the furnace and the amount of damage, at a downtime cost of several thousand of dollars per minute.
Lin, et al., U.S. Pat. No. 5,925,312, describe a device for removing tuyeres. The device utilizes a hydraulic cylinder attached to a rod having an attached hook. The device is moved into position in line with the tuyere, the hook engaged, and the hydraulic cylinder is activated to pull the tuyere from its tymp.
A hydraulic cylinder or ram is also employed in U.S. Pat. No. 4,087,084, to Meyers, to aid in the loosening of the tuyere from its tymp. But here, a hydraulic hammer, placed on a parallel axis with the rod, supplies vibration to the rod to aid in loosening the tuyere. The tuyere is then removed by action of the hydraulic cylinder. The hydraulic hammer provides vibration, but does not utilize the force of the hammer to pull the tuyere.
Malliet describes tuyere removal devices and movable supports to utilize the device. U.S. Pat. No. 5,127,633 describes the device with an air percussion hammer mounted co-axial with a double-piston ram and cylindrical rod mounted therein. The rod has a notch or hook at the end gripped by the ram. Malleit, in U.S. Pat. No. 4,266,907, mounts the device onto a self-propelled vehicle. The co-axial arrangement of the hammer and rod provides a reciprocating impact onto the tuyere, but the energy provided by the air percussion hammer is in a forward, pushing direction instead of the desired pulling direction.
Other existing tuyere removal methods may be entirely manual process and involve multiple operators manoeuvring a charge cart with a counterweighted component handling means and rope system to haul the tuyere out of the furnace wall. This method often takes several attempts and injury to operators is not uncommon. More automated systems for tuyere removal utilize hydraulic cylinders to pull the tuyere, but attached hammers are used either to vibrate the removal tool or push the tuyere.
A need for a removal device and method that quickly and easily pulls the tuyere from its tymp, reducing downtime, as well as preventing operator injuries, is desired.